Rolling of titanium base alloys



United States Patent This invention relates to rolled titanium base alloy materials.

with sheets of pure titanium about 0.06 inch thick by weldalloy containing 2.5% carbon was clad on opposed faces ing the cladding under argon to the ingot at the edges. The ingot was then hot rolled with the cladding presented to the rolls at a temperature of 900 0., about passes being necessary to reduce the thickness of 0.06 inch thick of which the cladding then totalled about 0.006 inch. The losses during the process by the grinding away of cracked edge portions of the rolled ingot between passes through the rolls were negligible. Test results on the final rolled product are shown in Table I.

TABLE I Results of Tests on 0.06 in. Thick Specimens of Clad T itanium-2.5 Carbon Alloy Rolled Sheet Heat Treatment Tensile 0.1% Modulus of Test Cooling Strength, Proof Elonga- Elasticity Piece Medium, tons per Stress, tion, E l0-,

Tempera- Time in w.q.: water sq. in. Tons per percent; lb. sq. in.

ture, 0 mins. quenched; sq. in.

f.c.: furnace cooled Commercially produced rolled titanium base alloy materials such as for example rolled sheets of titanium alloys consisting of a majority of titanium and about 8% manganese, or about 6% aluminum and about 4% vanadium, having one outstanding disadvantage compared with alternative sheet materials of similar specific strength such as stainless steels and nickel base alloys, namely their relatively low specific elastic modulus which may be expressed as the ratio of Youngs modulus (E) or the shear modulus '(G) to the specific gravity of the material.

One proposed method for improving the low specific elastic modulus of titanium base alloys is the addition of alloying elements such as carbon and/or boron or other similar elements which form stiff second phases in the alloys.

However when the carbon or boron content rises to even the low figure of 1.5% and 1% respectively, at which figure no advantageous increase in specific elastic modulus of the rolled material is achieved, successful rolling is quite impracticable except on the most limited experimental scale.

The present invention provides a new technique for rolling titanium base alloys containing an element such as carbon and/or boron which form a stiff second phase in the alloy and consists in cladding a workpiece of the alloy with relatively thin sheets or plates of ductile titanium or titanium alloy which will combine with the base alloy and hot rolling the workpiece with the cladding presented to the rolls. For most purposes it is highly desirable that the cladding should be initially welded to the workpiece at the edges, preferably by an arc welding process under an inert gas such as argon.

The temperature of rolling varies with the nature of the base alloy and in general isabove 800 C.

The presence of the cladding prevents the formation of surface cracks which in the absence of the cladding would not heal because they become oxidised.

Several examples according to the invention will now be described.

In a first example according to the invention a 2.5 inch diameter, 0.675 inch thick 300 gm. ingot of titanium base In a second example a gm. 1% inch diameter ingot of titanium base alloy containing 2% boron was clad as in Example I, and then reduced without difficulty by hot rolling at 900 C. with the cladding adjacent the rolls to 0.06 inch thick. Test results on the final product are shown in Table II.

TABLE II Results of Tests on 0.06 in. Thick Specimens of Clad Titanium-2% Boron Alloy Rolled Sheet In a third example, an ingot as in the first example, 0.675 inch thick, was clad with pure titanium sheets which were welded to the ingot at the rim, the sheets totalling about 6% of the thickness of the clad ingot. The ingot was then hot rolled at 900 C. and the overall thickness reduced to 0.5 inch, the cladding then totalling about 4% of the thickness. Rolling proceeded without difficulty and the light trimming or grinding of the rolled ingot between passes through the rolls resulted in negligible losses.

Ina fourth example a workpiece of titanium base alloy material containing aluminum, molybdenum and 1% boron, was clad with pure titanium sheets 0.017 inch thick welded to the workpiece at the edge under argon as in the case of the first example, and hot rolled at a temperature of 1000" C. in to sheet material. The rolling reduced the initial thickness of 0.65 inch to 0.065 inch in about 20 passes through the rolls and slightly raised the Vickers diamond hardness figure from an average value of about 312 to about 3.25. Several strip specimens were prepared from the rolled sheet and, for the purpose of comparing the bend ductility of the clad and unclad material, the cladding on some of the specimens was dissolved entirely away by pickling in a dilute hydrofluoric and nitric acid solution. The clad and unclad specimens were then subjected to bend tests at room temperature around formers of various radii of curvature. In the case of the clad strip specimen the strip bent readily round a former having a radius of curvature of 3 /2 times the thickness of the strip whereas the unclad strip failed in all attempts to bend it round a former having a radius of curvature as large as 8 times the thickness of the strip.

It will therefore be seen that the invention provides the means of rolling titanium base alloys containing 1.5% of carbon or 1% of boron or more of these or like stiff second phase forming elements as is necessary to give a high specific elastic modulus to the alloy, as Well as the means of maintaining at a high level bend ductility which would otherwise be adversely affected by these elements.

It is to be noted that the abovementioned ductile cladding alloy may be of titanium base alloy such as one containing 5% aluminum, also that the initial cladding of the workpiece may be performed by depositing layers of titanium on the surfaces by a shielded arc welding process.

We claim:

1. A method of working a titanium base alloy initially possessing good rolling properties but modified by the addition of a strengthening element selected from the group consisting of carbon and boron forming a stiff second phase in the alloy and imparting to it a high specific elastic modulus and bad rolling properties which method comprises Welding to opposed faces of a workpiece of the alloy under inert conditions a cladding of thin plates of ductile material selected from the group consisting of ductile titanium and titanium alloys and hot rolling the workpiece in air with the cladding presented to the rolls.

2. A method as claimed in claim 1 comprising initially welding plates of cladding to the workpiece under an inert gas shield before rolling.

3. A method as claimed in claim 2 comprising initially welding the plates to the workpiece only in the peripheral marginal region under an inert gas shield before rolling.

4. A method as claimed in claim 1 comprising depositing the cladding on the workpiece by a shielded arc welding process in which an inert gas is continuously supplied to the welding zone.

References Cited in the file of this patent UNITED STATES PATENTS 2,786,265 Keay Mar. 26, 1957 2,798,843 Slomin July 9, 1957 2,847,302 Long Aug. 12, 1958 2,858,600 Vigor Nov. 4, 1958 2,906,008 Boegehold Sept. 29, 1959 OTHER REFERENCES Brazing Titanium to Titanium and to Mild and Stainless Steels, by Lewis et -al., WADC Technical Report 52313, Part 2, December 1953, Wright Air Development Center, pages 1-9.

Progress Report on Cold Rolled Alloys, Report No. 16, Progress Report for June 1948, by P. R. Mallory (9 pp.) Memo No. 8000-M435.

Roll "Cladding of 'Base Metals With Titanium, WADC Report 53-502, December 1953. 

1. A METHOD OF WORKING A TITANIUM BASE ALLOY INITIALLY POSSESSING GOOD ROLLING PROPERTIES BUT MODIFIED BY THE ADDITION OF A STRENGTHENING ELEMENT SELECTTED FROM THE GROUP CONSISTING OF CARBON AND BORON FORMING A STIFF SECOND PHASE IN THE ALLOY AND IMPARTING TO IT A HIGH SPECIFIC ELASTIC MODULUS AND BAD ROLLING PROPERTIES WHICH METHOD COMPRISES WELDING TO OPPOSED FACES OF A WORKPIECE OF THE ALLOY UNDER INERT CONDITION A CLADDING OF THIN PLATES OF DUCTILE MATERIAL SELECTED FROM THE GROUP CONSISTING OF DUCTILE TITANIUM AND TITANUM ALLOYS AND HOT ROLLING THE WORKPICE IN AIR WITH THE CLADDING PRESSENTED TO THE ROLLS. 